As methods for repelling harmful insects to human bodies, for example, blood-sucking insects as mosquitoes, lice and mites, there is a method in which such chemicals as dimethyl phthalate, 2-ethyl-1,3-hexane-diol and indalone are applied to the skin singly or in combination. Recently, as a new type of the insect controlling material, there has been developed an insect controlling sheet comprising a base material such as paper or fabric impregnated or surface-coated with an insecticide. The flies, mites, cockroaches and other insects have been got rid of by scattering the aerosol agents of pyrethroid insecticide or spraying the organic phosphoric insecticide. However, these practices are poor in remaining effects, and so want repetitions. Places treated with the insecticides are polluted and undesirable to the human health, and it is not preferable to use such agents in the places dealing with the foods.
Further, in the food firms of the large scales, fumigation treatments are performed with methyl bromide, chloropicrin or aluminium phosphide. But these chemicals are a powerful medicine and a specific poison and have a high toxicity to men and beasts. Therefore, experts will have to be hired to treat them on holiday and the workers must keep away therefrom for a long time. The above are not easy practices as are ordinarily performed.
Recently there have been developed a repellent material passing a weak electric current, but this is inferior in practice and troublesome in handling.
However, with developing of the standard of living, feeling of cleanness is required, and hence not only intrusion of the insects into places for handling the foods or living spaces but also scatterings of dead bodies of the insects in these places are hated. Moreover, with rapid developments of electronics or the medical industry, a high degree of cleanness is required in precision machines per se or spaces where these precision machines are handled. However, the above-stated insecticidal material for controlling insects often cause scattering of dead bodies of the insects and fail to satisfy the above requirement. Accordingly, a development of a repellent material has been eagerly desired, which has a high effect of preventing the insects from gathering to an applied place, and shows a good durability of this effect and an appropriately controlled chemical releasing property.
In order to enhance the repellent capacity, it is important that the effect of the active chemical should be increased and furthermore the density of the chemical to a base material should be increased and the chemical should be gradually vaporized into an outer space. A product formed by coating a base material with a mixture of a controlling agent and a paint is known. However, the thickness of the coating is limited and even if the repellent chemical is incorporated at a high density, the total amount of the chemical is not increased and the repellent effect is limited. Moreover, if the chemical density is too high, the properties of the coating are degrated. Therefore, there may be assumed a method in which a relatively thick base such as a fabric or paper is impregnated with an active chemical at an appropriate density. According to this method, however, the gradually releasing property cannot be controlled for a long period of time. Therefore, required is a product in which an active chemical is contained in an appropriate amount and the component of a base material has such a chemical and physical affinity with the active chemical that the gradually releasing property is controlled. Moreover, this insect repellent product should be molded into a body capable of agreeing to the shape or configuration of a place or space where the product is set.
As the method for meeting the above requirements, there has been a method in which a repellent, an insecticide, a mildewproof agent, a perfume and the like are incorporated into general purpose thermoplastic resins such as polyethylene, polypropylene and polyvinyl chloride. Moreover, as the method for increasing the density of the active chemical, there has been a method in which chemicals are supported on fillers of these plastics.
These thermoplastic resins have ordinarily a melting point higher than 100.degree. C., and therefore, in a method in which the active chemical is kneaded into a melt of a thermoplastic resin, decomposition or evaporation of the chemical is readily caused. Even if the amount of the chemical to be decomposed or evaporated is small, the amount is increased when the operation is continued for a long period of time, and this method is not practical in view of the safety and efficiency process. For transpiration of the chemical from the surface of the base, it is preferable that the chemical per se should be a substance which is liquid at a room temperature and has a relatively high vapor pressure, and a chemical having a high effect has an especially high transpirability at the room temperature. If a large amount of such a chemical is kneaded into a plastic material having a high melting point, a violent bleeding to the surface is caused simultaneously with decomposition of the chemical.
Under the above mentioned background, the inventors made researches on insect repellent materials, and found that chlorinated polyethylene had a very good affinity with an amide type repelling ingredient of liquid at the room temperature, the content of the active ingredient in the chlorinated polyethylene could be increased, since the chlorinated polyethylene was powdery, it could be impregnated homogeneously with the amide type repelling ingredient, and the chlorinated polyethylene impregnated with the active ingredient could be advantageously formed into good granules for hot molding.
That is, since the chlorinated polyethylene is powdery and has the strong affinity with the amide repelling ingredient, the amide repelling ingredient can be contained much and uniformly, with which a thermoplastic elastomer is mixed. Since the thermoplastic elastomer has less affinity with the amide repelling ingredient than the chlorinated polyethylene, the ratio of the chlorinated polyethylene and the thermoplastic elastomer is controlled, thereby enabling to control the gradually releasing property of the amide type repelling ingredient. Thus, this invention has been accomplished.